The world of freelancing is different than the traditional path of going to college to get employment. In college, the general idea is that you spend 4 or more years learning a wide set of skills. Sometimes you'll gain a deep understanding of a few skills, but more often you'll just get a wide exposure to many skills.
And then you'll graduate, your ability to learn how to learn will be your greatest asset. Still, a few of those skills you learned will be directly transferrable, and those specific skills will help you to get hired.
But freelancing is different. If you know an employer wants a specific set of skills then you can focus on learning just those skills. You don't need to spend the time learning subjects that the employer isn't interested in, and in just a few months of focused learning you can have a few projects, samples, and a portfolio that showcases those specific skills.
This means you are more "agile" as a freelancer. It means that you can switch specialties in the fraction of a time it would take you to change your college major. It also means that you don't have to get worked up about what specialty to choose because you can always change.
For instance, say you choose iOS development thinking that you'll love making apps. But what happens if you don't like it? What happens if you realize you don't like programming anymore, your apps don't sell, and, the app store is a pain to work with? Then you can pivot. You could even switch focuses completely, and choose a niche in content writing for small businesses. Sure you might need to spend more time learning some more skills, but that's okay. Just pivot, dive in, and soon enough your skills will be proficient enough that you can sell them.
So, don't fret. Don't worry. Just pick something and get started. You can always change your focus later.